1. Technical Field of the Invention
The present invention relates to a method and apparatus for controlling a paging mode wherein paging data are RAKE-received by a Code Division Multiple Access (CDMA) wireless telephone terminal.
2. Description of the Prior Art
In a wireless telephone terminal, paging data reception is not continuously monitored in a paging mode in order to reduce a power consumption. More specifically, the wireless telephone terminal operates only a minimum circuit required for receiving paging data every paging cycle in which the base station intermittently outputs paging data. Upon a completion of the reception of the paging data, the wireless telephone terminal switches off the paging mode and switches on a sleep mode in which a power supply for a receiving circuit for receiving the paging data is turned off. Every arrival of a paging cycle, the wireless telephone terminal operates only a minimum circuit required for receiving paging data, and, upon completion of the reception of the paging data, the wireless telephone terminal repeats an operation for shifting the paging mode to the sleep mode.
In the sleep mode, only a circuit for measuring a paging cycle is operated. A system clock required for transmitting and receiving operations of the wireless telephone terminal has a high resolution and consumes electric power very much. Therefore, in order to measure the paging cycle, a paging clock having a relatively low resolution and a small power consumption is used. For example, the paging clock is 32 kHz or 32.768 kHz.
In the sleep mode, an offset of a clock count having a low resolution is estimated. Therefore, a high resolution system clock is switched on before several pulses of the low resolution paging clock. Thus, the paging data are received on the basis of the system clock.
An excessive power consumed by about 31.25 μsec to 100 μsec corresponding to the time period of several clocks of 32 kHz can be neglected, because time required when the system clock starts to receive paging data is about 100 msec.
A next-generation portable wireless telephone system International Mobile Telecommunication-2000 (IMT-2000) employs the CDMA wherein transmission data are subjected to spread spectrum modulation by using a pseudo-noise code having a frequency bandwidth wider than that of the transmission data.
A signal transmitted from the base station is reflected and diffracted by mountains, buildings, and the like to reach a portable wireless terminal through a plurality of transmission paths. Therefore, the signal received by the portable wireless terminal consists of a plurality of waves. Therefore, as a receiving modulation system of the portable wireless terminal, a RAKE receiving system is used. In the RAKE receiving system, a received signal converted from a Radio Frequency (RF) bandwidth to a base band is despread, so that a plurality of waves included in the received wave are separated. The separated signals are combined to obtain a demodulation output of the received signal.
A delay profile is formed to perform RAKE receiving, and a wireless transmission path is searched on the basis of the delay profile. The position of the searched transmission path must be subjected to RAKE combining. The delay profile is obtained by plotting delay times of radio waves reaching a reception point on an abscissa, and plotting the powers of the radio waves on an ordinate. A delay profile forming range used for RAKE receiving is generally about several tens μsec.
However, the rise up of a paging cycle measured by the paging clock does not occur simultaneously when the paging data arrive, because a paging clock having a low resolution is used to measure a paging cycle. In consideration of this error, the time range for forming the delay profile in the paging mode is 50 to 100 μsec or less of the width of the paging clock plus several tens μsec which is a time range for forming a delay profile in the speech mode.
Further, in the paging mode, a memory size required for the delay profile must be several times larger than that required for a speech mode.